Machinery and systems for the production of paper bags or carrier bags comprising various stations and equipment for the shaping and production of the bag, obtained by cutting and folding a strip of paper or other material, and one or more devices, commonly known as handle-forming machines, for shaping and attaching the handles, are known of.
Various types of handle-forming machines are known of which envisage operations of unwinding one or more paper and/or cord strips, from which each handle is made, of folding and cutting said strip to size to form each handle, and applying the handle to the bag or in continuum, to the roll of paper which the bag will be made from.
The handle-forming machines of the prior art have many drawbacks and disadvantages.
In particular, the handle-forming machines applying handles in continuum to the roll of paper which the bags will subsequently be made from are extremely complicated from a mechanical point of view and, in addition, given their functioning, are subject to jamming and accidental interruption of the manufacturing process.
In fact, as the production speed increases, the risk of a single handle not being perfectly attached to the roll of paper, with the risk of the detached or partially detached handle getting jammed in the mechanisms of the handle-forming or bagging machine and causing dangerous obstruction, increases exponentially.
Such obstructions may not only lead to prolonged downtime of the machine but also to damage of one or more parts of the machine itself.
Currently the production speed of paper or similar bags with a flat bottom is approximately 1000 pieces per minute, while the production speed of paper or similar bags with a square bottom is slower, about 150 pieces a minute.
Such production speed is not supported however by the known handle-forming machines, which need to keep the speed of shaping and attaching the handles to lower levels so as to prevent such risks of jamming.
Handle-forming machines for making so-called strap handles, that is each comprising a segment of paper or similar, folded once or more in a longitudinal direction, to form a linear strap are also known of. The end sections are then folded in relation to the central section to form a substantially U-shaped strap. Said strap handles are attached to the roll of paper after applying glue to the sides folded into a U and to a transversal reinforcement patch of said sides folded into a U.
To make the strap type handles, the handle-forming machine is fed with one or more strips of paper, which are usually folded once or more, as many as four times in a longitudinal direction, to make a more rigid strip.
The continuous strip is cut to size and grasped by rotating drums with grippers which cause folding of the strap. The strap is then rotated and attached to the preformed bag or to the roll of paper which the bag will be subsequently made from, by a plurality of drums.
To prevent the strap from shifting or moving away from the surface of the drum or drive belt during the exchange between various drums, suction devices are used inside the drums or under the belts to keep said straps perfectly adherent to the surface of the drum or belt.
In addition, on account of the presence of said sliding belts, the speed of the handle-forming machines cannot be increased beyond determined limits, which would entail excessive mechanical stress on the belts themselves, with the risk of breakage.
In the known handle-forming machines the rollers must work in perfect synchrony, with the maximum precision, to limit the amount of jamming, which is however inevitable.